The present invention relates to a reflective type liquid crystal display device capable of photoelectrically converting a part of incident light to be supplied with power, and a method for manufacturing same. More particularly, the invention relates to a reflective type liquid crystal display device usable for timepieces, handy phones, portable information terminals and so on.
Liquid crystal display devices are broadly used as display panels of appliances in various applications, due to many superior features including thin size and low power consumption.
The reflective type LCD is operable on extremely reduced power because it does not require a light self-emitting device such as a back light source. Meanwhile, there is a tendency toward decreasing power consumption of an LSI as a principal component for constituting a small-sized portable electronic appliance. Due to this, there is also a tendency, in an LSI power source, to replace the conventional battery for the reflective type LCD by a photovoltaic element. The photovoltaic element in general often uses a photoelectric converting device called a solar battery. Small-sized portable appliances built with a reflective LCD and solar battery, including a timepiece, desk-top calculator and radio, have been put into marketing in today's marketplaces.
The conventional small-sized portable appliance structure incorporating a reflective LCD and photovoltaic element has the following disadvantages. In the case of the card-type desk top calculator for example, if the display section is enlarged in area in order to facilitate display reading, the solar battery section area is decreased thus resulting in insufficient power to operate the card desk-top calculator. Also, if the key input section area is increased to facilitate input operation, the solar cell section area is similarly decreased resulting in insufficient power for operating the card desk-top calculator. Consequently, the solar battery section area is preferably made as small as possible in respect of designing a card desk-top calculator with its inherent functions fully reflected.
In the case of the digital watch, if the display section area is increased to make easy display reading, the solar battery section area is decreased resulting in insufficient power to operate the digital watch. Also, the existence of broad blackish solar cell in a digital watch surface makes design rustic. This makes the fashionability essential for a watch poor, considerably reducing its commodity value.
This problem is similarly true for the conventional small-sized portable appliance incorporating a reflective LCD and solar battery. It can be considered, as a measure for solving this problem, to stack the reflective LCD and the solar battery.
There is a considerable concrete method wherein a solar battery transmissible of light to generate power is placed over a reflective LCD. Such a solar battery may be a see-through type solar battery having a plurality of fine pores. However, this method includes the following problems.
If it is assumed the see-through type solar battery has a light transmission rate of 30%, the structure with the solar battery on the reflective LCD has an optical path duplicated in transmission and reflection. This reduces the brightness of the reflective LCD to about 9% as compared with a usual using state, making extremely dark. Further, the reflection on the surface solar battery decreases visibility. Accordingly, in this case nothing is obtained other than dark and low visible display wherein the power generating efficiency of the solar battery decreases to 50% or lower as compared with that of the usual solar battery.
Meanwhile, another method can be considered that a solar battery 42 is provided at the back of a light-scattering liquid crystal device 41 as disclosed in JP-A-8-160380 (FIG. 4).
In addition to the above method, it is possible to both satisfy the reduction in power generating efficiency and the lessen deterioration in display quality; by providing between a light scattering liquid crystal display device 41 and a solar battery 42 a reflective layer having a characteristic with a light reflectivity of 20-70% to absorb almost no visible portion of light in a particular range but transmit almost the remaining visible and near infrared portions of light, and providing at the back a solar cell 42 having a spectral sensitivity worse in the visible portion of light.
The conventional structure with a stacked reflective LCD and solar battery has the following disadvantage.
That is, where the solar battery is placed in front of the reflective LCD, display quality degrades with decreased power generating efficiency. Meanwhile, if the solar battery is arranged at a back of the light scattering reflective LCD, it is possible to satisfy the reduction both in power generating efficacy decrease and in decrease of display quality. However, because the light scattering liquid crystal is difficult to effect high time divisional drive, an LCD sufficient in information volume cannot be realized unless combined with active elements such as MIM or TFT, resulting in expensive in cost as compared with the simple matrix panel.